Apparatus for zone refining

ABSTRACT

Improvements in apparatus for zone refining polycrystalline semiconductor rods to produce monocrystalline semiconductor rods are disclosed. In the apparatus, an inductive heating chamber is employed which has a longitudinal dimension independent of the length of the polycrystalline semiconductor rod to be processed. The longitudinal dimension of the induction heating chamber is limited only by considerations of the space required for the RF induction heating coil and related apparatus which must be mounted within the chamber, the viewing space required for the operator to observe the zone refining process, and the heating effect on the structures above and below the chamber. First and second gas tight bellows are provided which, respectively, surround the rod holder and the seed holder. One end of each of the first and second bellows is releasably and sealingly attached to the induction heating chamber, while the other end of each of the first and second bellows is attached to the base of the rod holder or seed holder, respectively. These bellows expand and collapse with the relative movement of the rod holder and seed holder with respect to the induction heating chamber. Moreover, with the rod holder displaced from the induction heating chamber, the first bellows may be detached from the chamber and collapsed to facilitate mounting a polycrystalline semiconductor rod to be refined in the rod holder, and when the refining process is complete and the seed holder is displaced from the chamber, the second bellows can be detached from the chamber and collapsed to facilitate the removal of the refined monocrystalline rod from the seedholder. In order to protect the lower most bellows from molten semiconductor, a plurality of telescoping metallic cylinders are positioned within the bellows and concentric therewith.

BACKGROUND OF THE INVENTION

The present invention generally relates to apparatus for zone refiningpolycrystalline semiconductor rods to produce monocrystallinesemiconductor rods, and more particularly to improvements in saidapparatus which permit the processing of larger diameter rods, andlonger rods, without unduly increasing the overall height of theapparatus.

Conventional apparatus for zone refining includes an induction heatingchamber. A rod holder for holding a polycrystalline semiconductor rod tobe refined comes into the chamber from the top. A seed holder forholding a semiconductor seed crystal comes into the chamber from thebottom. The chamber has a door with a window, the window being necessaryto permit the operator to watch the zone refining operation especiallyduring the initial stage when the seed crystal is fused to the moltenend of the semiconductor rod.

In a typical apparatus, a polycrystalline semiconductor rod on the orderof 110 cm long can be refined. Such a rod is attached to the rod holderat its upper end, and a 6 mm diameter seed crystal is attached to theseed holder. A heavy RF induction heating coil of suitable design ispositioned near the middle of the induction heating chamber. The chamberis purged and then either evacuated or filled with an inert gas, such asargon. The rod holder and rod are moved down so that the free end of therod approaches the RF induction heating coil. The RF coil inductivelyheats and melts the bottom or free end of the semiconductor rod until agood molten droplet of semiconductor is formed. At that point, the seedcrystal and seed holder moves up to the molten end of the rod within theheating zone of the RF coil. The seed crystal fuses and is pulled awayto create a taper at the molten end of the semiconductor rod.Thereafter, the zone of the melt is moved up the rod by moving both therod and the seed crystal downward. Relative movement between the seedholder and rod holder controls the diameter of the refinedmonocrystalline semiconductor rod and, in addition, the rod holder andseed holder can be independently rotated as both move downwardly withrespect to the induction heating chamber.

In order to melt the semiconductor rod, the RF power required issubstantial, and losses are minimized by providing the tank circuit justoutside the induction heating chamber at the same level as the RF coil.This permits the power leads in the form of a coaxial cable between thetank circuit and the RF coil to be as short as possible.

The minimum height for conventional zone refining apparatus is at leastfour and often five times the length of the polycrystalline rod to berefined. The induction heating chamber itself must be twice as long asthe rod to accommodate the full movement of the rod through the RF coil.The fully extended positions of the rod holder and the seed holder areeach equal to the length of the rod at a minimum.

Since the start-up time of a zone refining operation is very timeconsuming and requires constant monitoring by a highly skilled operator,a determined effort has been made to process larger and larger rods.Unfortunately, the overall height requirements for the zone refiningapparatus poses a serious problem. In some cases, the size of thebuilding housing the apparatus would have to be increased, an expensewhich may not be justifiable. Moreover, tall structures become laterallyunstable, thereby posing serious problems of support and dimensionalstability.

One possible solution is to move the RF induction heating coil ratherthan the semiconductor rod. If this solution were done then, in theoryat least, the induction heating chamber could be made somewhat longerthan the rod to be refined. The chamber would have to be longer than therod to allow the starting position of the RF coil to be within view ofthe operator, to accommodate the rod holder and seed holder, and for anyadditional travel space required for the refining process. While thissolution is at first appealing, it must be remembered that in order tomelt larger diameter semiconductor rods, substantially high power at avery high frequency (from 2 to 4 megahertz) must be coupled into the rodby the induction heating coil. This means that if the RF coil is moved,a heavy flexible coaxial cable, or some other applicable means, must beused to connect the tank circuit to the RF coil. The expense and otherproblems, especially large power losses and possible arcing in thecoaxial cable, make this approach to the problem very unattractive. Evenunder the best of circumstances, the cables needed to carry the powerrequired to the RF coil will ordinarily result in a loss of 30 to 50percent of the power; these numbers could vary depending upon theelectrical circuits and machine design.

According to the present invention, the zone refining apparatus isprovided with an induction heating chamber the longitudinal dimension ofwhich is not determined by the length of the rod to be refined, butinstead is limited only by considerations of space for the RF coil andrelated apparatus which must be mounted within the chamber, viewingspace for the operator, and the heating effect on the structure aboveand below the chamber. More specifically, the semiconductor rod is movedand the RF coil is stationary, just as in the conventional apparatus.However, the semiconductor rod extends above the induction heatingchamber initially and below the chamber at the conclusion of therefining process. An upper metal bellows extends from the top of the rodholder to the top of the chamber. A similar lower metal bellows extendsfrom the bottom of the seed holder to the bottom of the chamber. The twobellows thus keep the working space both gas and vacuum tight. Atelescoping group of steel cylinders are placed inside the lower bellowsto protect the lower bellows from any molten semiconductor which maydrop from the melt zone. The length of the telescoping cylinderscollapsed is the same as the length of the bellows collapsed. Eachbellows terminates in a flange that is bolted to the induction heatingchamber. These bolts are easily undone for insertion and removal of thesemiconductor rod.

To load the apparatus according to the invention, the upper bellows isextended fully to place the rod holder at its upper most position abovethe induction heating chamber. The upper bellows is then unbolted fromthe chamber and compressed from the bottom up thereby permitting thesemiconductor rod to be fastened to the rod holder with the lower orfree end of the semiconductor rod just projecting within the heatingchamber. The upper bellows is then extended and re-attached to the topof the chamber. In a similar operation, the semiconductor seed crystalis attached to the seed holder. Once the lower bellows is attached tothe bottom of the induction heating chamber, the lower bellows iscompressed upward so that the seed crystal is in position to begin thezone refining process. During the zone refining process, the rod holderand seed holder move downwardly causing the upper bellows to compressand the lower bellows to expand. At the end of the refining process, thebottom bellows is unbolted from the bottom of the heating chamber andcompressed downwardly permitting easy access to the refinedmonocrystalline semiconductor rod which is removed from the seed holder.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the following detaileddescription taken together with reference to the drawings, in which:

FIG. 1 is a cross-sectional view of the apparatus according to theinvention showing the upper bellows fully expanded and the lower bellowsfully compressed at the beginning of the refining process;

FIG. 2 is a cross-sectional view of the apparatus according to theinvention showing the upper bellows fully compressed and the lowerbellows fully expanded at the end of the refining process;

FIG. 3 is a side view of the apparatus according to the inventionshowing in more detail the traversing mechanisms;

FIG. 4 is a fragmentary side view of the upper portion of the apparatusillustrating the position of the upper bellows to permit loading asemiconductor rod to be refined; and

FIG. 5 is a fragmentary cross-sectional view of the lower portion of theapparatus showing the protective telescoping cylinders within the lowerbellows.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein the same reference numberals referto identical or corresponding parts throughout the several views, theframe for the apparatus comprises a base plate 10, a top plate 11 andfour supporting rods 12, 13, 14, and 15 as shown; for example, in FIGS.1 and 3 of the drawings. An induction heating chamber 16 is fixedlyattached to the supporting rods approximately midway between the baseplate 10 and the top plate 11. The induction heating chamber 16 isdefined by a top 17 having an opening therein, a bottom 18 having anopening therein, and a side wall 19. The top 17 and bottom 18 aresubstantially identical being generally rectangular in shape and fixedlyattached to the supporting rods 12, 13, 14, and 15. The spacing betweenthe top 17 and the bottom 18 is relatively close being determined bymechanical considerations which are discussed in more detailhereinafter. The side wall 19 is generally cylindrical in shape havingoutwardly projecting flanges at either end. These flanges are attachedto the top 17 and the bottom 18 to form a gas tight seal therebetween.This may be done by welding, bolting with a gasket or any otherconventional means. At what may be considered the front of theapparatus, the side wall 19 is provided with a transparent window 20 topermit the operator to observe the zone refining process.

Two guide rods 21 and 22 are journaled into the base plate 10 and thetop plate 11. Alternatively, each guide rod 21 and 22 may be dividedsuch that guide rods 21a and 22a are journaled into the base plate 10and the bottom 18 of the induction heating chamber 16 while guide rods21b and 22b are journaled into the top plate 11 and the top 17 of theinduction heating chamber 16. A rod holder carriage assembly 23 isslidably mounted on the guide rods 21 and 22. The carriage assembly 23comprises a carriage plate 24 having journaled bearings 25 and 26through which the guide rods 21 and 22 pass. A cup-shaped member 27opening downwardly and having an outwardly projecting flange is mountedwithin an opening formed in the carriage base 24 so that the closed endof the cup-shaped member 27 is flush with the top surface of thecarriage plate 24. An electric motor 28 is centrally mounted on theupper exterior surface of the cup-shaped member 27. The rotating shaftof the electric motor 28 projects into the cup-shaped member 27 and hasattached thereto a rod holder 29. The cup-shaped member 27 and theelectric motor 28 are sealed so as to form a gas tight structure. Therod holder 29 is provided at its lower most end with a suitableappliance 30 for gripping or holding a semiconductor rod which is to berefined.

The opening in the top plate 17 of the induction heating chamber 16 isprovided with a short cylindrical fitting 31 having an outside diameterequal to the inside diameter of the opening in the top 17. This fitting31 is fixedly attached to the internal surface of the opening in top 17as by welding, bolting or the like to provide a gas tight seal. Thefitting 31 projects upwardly beyond the induction heating chamber and isprovided with an outwardly projecting flange. This flange mates with abellows carriage assembly 32 which comprises a carriage plate 33 andjournaled bearings 34 and 35 through which the guide rods 21 and 22pass. The carriage plate 33 is bolted to the flange of the fitting 31,and a gas tight seal is provided by a compressed O-ring. A metallicbellows 36 is connected at its lower end to the bellows carriage plate33 and at its upper end to an annulus 37 which mates with the outwardlyprojecting flange of the cup-shaped member 27. The annulus 37 may bepermanently attached to the outwardly projecting flange of thecup-shaped member 27 by welding, but preferably the annulus 37 and theoutwardly projecting flange of the cup-shaped member 27 are boltedtogether with a gas tight seal such as a compressed O-ring so that thebellows 36 may be removed and replaced if required.

A similar structure is provided in the bottom portion of the apparatus.More particularly, a seed holder carriage assembly 38 is slidablymounted on the guide rods 21 and 22. The seed holder carriage assembly38 comprises a carriage plate 39 having journaled bearings 40 and 41through which the guide rods 21 and 22 pass. A cup-shaped member 42 ismounted within an opening in the carriage plate 39 so that it opensupwardly. The cup-shape member 42 is provided with an outwardlyprojecting flange and is mounted within the opening in the carriageplate 39 so that the closed end of the cup-shape member 42 is flush withthe lower surface of the carriage plate 39. An electric motor 43 ismounted on the exterior surface of the closed end of the cup-shapemember 42, and the rotating shaft of the electric motor 43 projects intothe cup-shape member 42. Again, the cup-shape member 42 and the electricmotor 43 are sealed to provide a gas tight structure. The rotating shaftof the electric motor 43 has a seed holder 44 attached to it. The seedholder 44 projects upwardly and is provided at its upper most end withan appliance 45 for mounting a semiconductor seed crystal.

The opening in the bottom 18 of the induction heating chamber 16 isprovided with a cylindrical fitting 46 which has an outside diameterequal to the inside diameter of the opening in the bottom 18. Thefitting 46 is welded, bolted or the like to the inside surface of theopening in the bottom 18 to form a gas tight seal. The fitting 46projects downwardly outside of the induction heating chamber 16 and hasan outwardly projecting flange. This flange mates with a lower bellowscarriage assembly 47 which comprises a carriage plate 48 and journaledbearings 49 and 50 through which the guide rods 21 and 22 pass. Thecarriage plate 48 is bolted to the outwardly projecting flange of thefitting 46, and a gas tight seal is provided by a compressed O-ring. Oneend of the bellows 51 is attached to the carriage plate 48, while theother end of the bellows 51 is attached to an annulus 52. The annulus 52is bolted to the outwardly projecting flange of the cup-shaped member42, and a gas tight seal is provided by a compressed O-ring.

In order to load a polycrystalline semiconductor rod to be refined, therod holder carriage assembly 23 is raised to its highest point along theguide rod 21 and 22. This is accomplished with the traversing mechanismshown in FIGS. 3 and 4. More specifically, a lead screw 53 is rotatablyjournaled at one end in the top plate 11 and at the other end in the top17 of the induction heating chamber 16. The screw 53 passes through butdoes not engage the carriage plate 33 of the bellows carriage assembly32. However, the carriage plate 24 of the rod holder carriage assembly23 is provided with a screw follower 54 through which the screw 53passes. The upper end of the screw 53 is provided with a pulley 55. Thepulley 55 is rotated and the screw 33 is in turn rotated by a belt 56which passes around a driving pulley 57. The driving pulley 57 ismounted on a shaft projecting out of the gear transmission 58. The geartransmission 58 is in turn driven by an electric motor 59 mounted to thetop plate 11.

Once the rod holder carriage assembly 23 has been moved to its uppermost position, the bellows carriage plate 33 can be unbolted from theflange of the fitting 31 and the bellows 36 collapsed to expose the rodholder 29. To accomplish this, there is provided a hydraulic motor 60attached to the support rods 13 and 15. The hydraulic motor 60 iscentrally located between the support rods 13 and 15 and moreimportantly it is centrally located between the guide rods 21 and 22. Asillustrated, the hydraulic motor 60 is a linear motor of conventionaldesign having a cylindrical housing 61 having a movable piston (notshown) housed therein. The piston moves upwardly or downwardly withinthe housing 61 under control of a pneumatic or fluid source in awell-known manner. The ends of the cylindrical housing 61 are sealedwith end caps 62 and 63. These end caps support pulleys 64 and 65. Acable 66 attached at either end to the piston within the cylindricalhousing 61 passes through seals in the end caps 62 and 63 and around thepulleys 64 and 65. A traverse fitting 67 is attached on the one hand tothe cable 66 and on the other hand to the bellows carriage assembly 32.Thus, as the piston in the cylindrical housing 61 moves downwardly, thecable 66 moves in a clockwise direction causing the bellows 36 to becollapsed.

With the rod holder carriage assembly 23 and bellows 36 in the positionillustrated in FIG. 4, a polycrystalline semiconductor rod to be refinedcan be loaded into the apparatus. This is done by attaching one end ofthe rod 68 in the appliance 30 at the end of the rod holder 29 so thatthe free end of the rod projects just into the induction heating chamber16 as illustrated in FIG. 1. Once the rod 68 has been attached to therod holder 29 by means of the appliance 30, the bellows 36 can be onceagain expanded by operating the hydraulic motor 60 so that the bellowscarriage plate 33 can be bolted to the outwardly projecting flange ofthe fitting 31. In a similar manner, the seed crystal 74 is mountedwithin the appliance 45 at the end of the seed holder 44. A linearhydraulic motor 80 collapses the bellows 51 and the seed crystal iseasily mounted. The bellows 51 can once again be expanded by operatingthe hydraulic motor 80 so that the bellows carriage plate 48 can bebolted to the outwardly projecting flange of the fitting 46. Once a gastight seal has been made, the volume within the induction heatingchamber 16 and the bellows 36 and 51 is purged with an inert gas, suchas argon, for gas refining or evacuated for vacuum refining. For gasrefining, the volume within the chamber 16 and the bellows 36 and 51 isfilled with an inert gas such as argon. To accomplish this, there isillustrated in FIG. 3 a conduit 69 which communicates with the interiorof the induction heating chamber 16 at one end thereof and is attachedat the other end thereof to a vacuum pump 70. It will, of course, beunderstood that other conduits and valving mechanisms to the inductionheating chamber 16 could be provided as may be required, but these arenot shown in the drawings in order to simplify the illustration of theoverall apparatus.

Within the induction heating chamber 16 is an RF induction coil 71 ofsuitable design. This induction heating coil 71 is centrally locatedwithin the chamber 16 and axially aligned with the rod holder 29 and theseed holder 44. The RF induction heating coil 71 is connected by meansof an electrical fitting 72 which projects into the induction heatingchamber 16 to a tank circuit which is enclosed in the housing 73. Thehousing 73 is mounted to but electrically insulated from the bottomsurface of the top 17 of the induction heating chamber 16.

At the beginning of the refining process, the rod holder carriageassembly 23 is moved downwardly so that the free end of the rod 68 isproximate to the RF heating coil 71. The coil 71 inductively heats andmelts the free end of the rod to form a molten droplet. The operatorobserves this through the window 20 of the chamber 16 and causes theseed holder carriage assembly 38 to be moved upwardly so that a seedcrystal 74 mounted in the appliance 45 at the end of the seed holder 44fuses to the molten droplet at the end of the rod 68.

The mechanism for moving the seed holder carriage assembly 38 isidentical with the mechanism for moving the rod holder carriage assembly23 and is illustrated in FIG. 3 as comprising a lead screw 75 passingthrough a screw follower 76 in the carriage plate 39. The lead screw 75is driven by an electric motor 77 mounted on the base plate 10 through abelt and gear transmission 78.

Once the seed crystal 74 has fused in the molten drop at the end of therod 68, then both the rod holder carriage assembly 23 and the seedholder carriage assembly 38 are progressively moved downwardly so thatthe rod 68 passes downwardly through the RF induction heating coil, andas a result the melt zone moves upwardly along the length of the rod 68.The rod holder carriage assembly 23 and the seed holder carriageassembly 39 can be moved at different rates or the same rate, and therod holder 29 and the seed holder 44 can be rotated by the electricmotors 28 and 43, respectively. When either the rod holder carriageassembly or the seed holder carriage assembly has reached its lower mostpoint, as illustrated in FIG. 2, the refining process is completed.After allowing sufficient time for cooling the now refinedmonocrystalline, semiconductor rod 79 can be moved from the apparatus.In order to accomplish this, the lower bellows carriage plate 48 isunbolted from the flange of the fitting 47, and the bellows 51 iscollapsed. A linear hydraulic motor 80 similar to hydraulic motor 60 isprovided for the purpose of collapsing and expanding the bellows 51 whenthe seed holder carriage assembly 39 is in its lower most position.Thus, the bellows 51 is collapsed in the same manner that bellows 36 iscollapsed in the illustration shown in FIG. 4. With the bellows 51collapsed, the refined monocrystalline semiconductor rod 79 can beeasily removed from the apparatus.

As will now be fully appreciated, the longitudinal dimension of theinduction heating chamber 16 is completely independent of the length ofthe semiconductor rod to be processed. Instead of having a longitudinaldimension which is twice the length of the rod to be processed as inconventional apparatuses of this type, the induction heating chamber 16can be reduced in longitudinal dimension to a practical absolute minimumdimension thereby greatly decreasing the overall height of the zonerefining apparatus while at the same time maintaining a stationary RFinduction heating coil position. The limiting conditions for thelongitudinal dimension of the induction heating chamber 16 areconsiderations of the space for the RF coil 71 and related apparatuswhich must be mounted within the induction heating chamber, the viewingspace for the operator as provided by the window 20, and the heatingeffect on the bellows 36 and 51 above and below the chamber 16. In orderto withstand the substantial temperatures generated in the zone refiningapparatus, the bellows 36 and 51 are preferably made of metal. Althoughmade of metal, the bellows are necessarily made of a light gauge metalin order to assure the required flexibility and, therefore, the lowerbellows 51 is susceptible to damage from molten semiconductor that maydrop from the melt zone. Additional protection from the substantialtemperatures may be provided for the apparatus by water cooling the wall19 of the induction heating chamber 16.

Reference is now made to FIG. 5 of the drawings which shows amodification of the basic invention which provides protection for thelower bellows 51. More specifically, a plurality of telescoping steelcylinders 81, 82, 83, and 84 are coaxially located within the bellows51. These steel cylinders are loose fitting and provided with matinginwardly and outwardly directed flanges. The largest cylinder 81 isattached in common with the bellows 51 at its upper end to the bellowscarriage plate 48. The cylinders 82, 83, and 84 have progressivelysmaller diameters with the smallest cylinder 84 being attached at itslower end about the base of the seed holder 44 to the interior surfaceof the cup-shaped member 42. Thus, it will appreciated that any moltensemiconductor dropping from the melt zone will fall harmlessly with thetelescoping steel cylinders 81, 82, 83 and 84 which provide completeprotection to the interior of the bellows 51. While four steel cylindershave been illustrated, it will be understood by those skilled in the artthat the number of telescoping cylinders will be determined by thedimensions of the bellows 51 in its collapsed and expanded conditions.In other words, when the bellows 51 is fully collapsed as illustrated inFIG. 1 and 3, the cylinders 81, 82, 83, and 84 will be fully telescoped,and when the bellows 51 is fully expanded as illustrated in FIGS. 2 and5, the cylinders 81, 82, 83, and 84 will be fully extended.

As this invention may be utilized for vacuum refining processes whereinthe refining chamber is evacuated as well as gas refining processeswherein the refining chamber is filled with an inert gas, it is to beunderstood that the wording "gas tight" is defined as being both gastight and vacuum tight. Thus, a gas tight seal or bellows is both gastight and vacuum tight.

Having described a preferred embodiment of the invention, it will beapparent to those skilled in the art that modifications and variationscan be made in the practice of the invention as defined in the appendedclaims.

What is claimed is:
 1. In an apparatus for zone refining polycrystallinesemiconductor rods to produce monocrystalline semiconductor rods, saidapparatus having an RF induction heating coil, a rod holder and a seedholder aligned vertically above and below said heating coil, said rodholder being adapted to hold one end of a polycrystalline semiconductorrod to be refined and said seed holder being adapted to hold a seedcrystal of said semiconductor, means for moving said rod holder relativeto said RF induction heating coil to bring the free end of thepolycrystalline semiconductor rod into proximity with said RF inductionheating coil to melt said free end, and means for moving said seedholder relative to said RF induction heating coil so that the seedcrystal contacts and fuses with the molten free end of thepolycrystalline rod, said rod holder and said seed holder thereafterbeing moved in the same direction relative to said RF induction heatingcoil so that the zone of the melt is moved along the length of thesemiconductor rod, the improvement comprising:an induction heatingchamber having said RF inductive heating coil fixed therein, saidinduction heating chamber having a longitudinal dimension indendent ofthe length of the polycrystalline semiconductor rod to be processed, afirst gas tight bellows surrounding said rod holder, one end of saidbellows being attached to said induction heating chamber and the otherend of said bellows being attached to the base of said rod holder, saidbellows expanding and collapsing with the relative movement of said rodholder and said RF induction heating coil, a second gas tight bellowssurrounding said seed holder, one end of said bellows being attached tosaid induction heating chamber and the other end of said bellows beingattached to the base of said seed holder, said bellows expanding andcollapsing with the relative movement of said seed holder said RFinduction heating coil, and a plurality of telescoping metalliccylinders surrounding said seed holder. within said corresponding secondgas tight bellows, the largest of the telescoping metallic cylindersbeing attached in common with said second bellows to said inductionheating chamber and the smallest of the telescoping steel cylindersbeing attached to the base of said seed holder, said plurality oftelescoping metallic cylinders serving to protect said second bellowsfrom molten semiconductor at all times when zone refining is takingplace.
 2. The improved apparatus for zone refining polycrystallinesemiconductor rods as recited in claim 1, wherein said one end of eachof said first and said second gas tight bellows are each releasablyattached to said induction heating chamber to facilitate mounting apolycrystalline semiconductor rod to be refined in said rod holder,mounting a seed crystal in said seed holder, and removing a refinedmonocrystalline rod from said seed holder.
 3. The improved apparatus forzone refining polycrystalline semiconductor rods as recited in claim 2,further comprising:first means attached to said one end of said firstgas tight bellows for collapsing said bellows when said rod holder isdisplaced from said RF induction heating coil to permit mounting apolycrystalline semiconductor rod to be refined in said rod holder, saidfirst means thereafter expanding said bellows to permit sealingattachment of said one end to said induction heating chamber, and secondmeans attached to said one end of said second gas tight bellows forcollapsing said bellows when said seed holder is displaced from said RFinduction heating coil to permit removing a refined monocrystallinesemiconductor rod from said seed holder and mounting a semiconductorseed crystal in said seed holder, said second means thereafter expandingsaid bellows to permit sealing attachment of said one end of saidinduction heating chamber.
 4. The improved apparatus for zone refiningpolycrystalline semiconductor rods as recited in claim 1, wherein saidinduction heating chamber is stationary and includes means forevacuating said chamber and said first and second gas tight bellowsafter said first and second gas tight bellows are attached to saidinduction heating chamber.
 5. The improved apparatus for zone refiningpolycrystalline semiconductor rods as recited in claim 4, wherein saidinduction heating chamber further includes means for filling saidinduction hating chamber and said first and second gas tight bellowswith an inert gas.
 6. In an apparatus for zone refining polycrystallinesemiconductor rods to produce monocrystalline semiconductor rods, saidapparatus having an RF induction heating coil, a rod holder and a seedholder aligned vertically above and below said heating coil, said rodholder being adapted to hold one end of a polycrystalline semiconductorrod to be refined and said seed holder being adapted to hold a seedcrystal of said semiconductor, means for moving said rod holder relativeto said RF induction heating coil to bring the free end of thepolycrystalline semiconductor rod into proximity with said RF inductionheating coil to melt said free end, and means for moving said seedholder relative to said RF induction heating coil so that the seedcrystal contacts and fuses with the molten free end of thepolycrystalline rod, said rod holder and said seed holder thereafterbeing moved in the same direction relative to said RF induction heatingcoil so that the zone of the melt is moved along the length of thesemiconductor rod, the improvement comprising:a stationary inductionheating chamber having said RF inductive heating coil fixed therein,said induction heating chamber having a longitudinal dimensionindependent of the length of the polycrystalline semiconductor rod to beprocessed, a first gas tight bellows surrounding said rod holder, oneend of said bellows being releasably attached to said induction heatingchamber to facilitate mounting a polycrystalline semiconductor rod to berefined in said holder and the other end of said bellows being attachedto the base of said rod holder, said bellows expanding and collapsingwith the relative movement of said rod holder and said RF inductionheating coil, and a second gas tight bellows surrounding said seedholder, one end of said bellows being releasably attached to saidinduction heating chamber to facilitate mounting a seed crystal in saidseed holder and removing a refined monocrystalline rod from said seedholder and the other end of said bellows being attached to the base ofsaid seed holder, said bellows expanding and collapsing with therelative movement of said seed holder and said RF induction heatingcoil, a plurality of telescoping metallic cylinders surrounding saidseed holder, within said corresponding second gas tight bellows, thelargest of the telescoping metallic cylinders being attached in commonwith said second bellows to said induction heating chamber and thesmallest of the telescoping steel cylinders being attached to the baseof said seed holder, said plurality of telescoping metallic cylindersserving to protect said second bellows from molten semiconductor at alltimes when zone refining is taking place, said first and second bellowsfurther including: first means attached to said one end of said firstgas tight bellows for collapsing said bellows when said rod holder isdisplaced from said RF induction heating coil to permit mounting apolycrystalline semiconductor rod to be refined in said rod holder, saidfirst means thereafter expanding said bellows to permit sealingattachment of said one end to said induction heating chamber, and secondmeans attached to said one end of said second gas tight bellows forcollapsing said bellows when said seed holder is displaced from said RFinduction heating coil to permit removing a refined monocrystallinesemiconductor rod from said seed holder and mounting a semiconductorseed crystal in said seed holder, said second means thereafter expandingsaid bellows to permit sealing attachment of said one end of saidinduction heating chamber, wherein said induction heating chamberfurther includes: means for evacuating said chamber and said first andsecond gas tight bellows after said first and second gas tight bellowsare attached to said induction heating chamber, and means for fillingsaid induction heating chamber and said first and second gas tightbellows with an inert gas.
 7. The improved apparatus of claim 6 whereinsaid induction heating chamber includes a water cooled wall.